Miniature actuator mechanism for intravascular imaging

ABSTRACT

The present invention relates to a new intravascular imaging device based on a Shape Memory Alloy (SMA) actuator mechanism embedded inside an elongate member such as a guide wire or catheter. The present invention utilizes a novel SMA mechanism to provide side-looking imaging by providing movement for an ultrasound transducer element. This novel SMA actuator mechanism can be easily fabricated in micro-scale, providing an advantage over existing imaging devices because it offers the ability to miniaturize the overall size of the device, while the use of multiple transducer crystals maximizes field of view. Also disclosed are methods of using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119 to U.S. ProvisionalApplication Ser. No. 60/678,676, filed May 4, 2005, titled “Multipletransducers for large field of view in intravascular ultrasoundimaging,” U.S. Provisional Application Ser. No. 60/677,944, filed May 4,2005, titled “Shape memory alloy (SMA) mechanism for side-lookingintravascular imaging,” U.S. Provisional Application Ser. No.60/710,304, filed Aug. 22, 2005, titled “Guide wire enabled withintravascular ultrasound imaging for interventional applications” andU.S. Provisional Application Ser. No. 60/711,653, filed Aug. 25, 2005,titled “Miniature mirror-based intravascular ultrasound imaging devicefor interventional applications,” and U.S. Provisional Application Ser.No. 60/781,786, filed Mar. 13, 2006, titled “Electrically drivenminiature intravascular optical coherence tomography imaging device,”the entire contents of each of which are incorporated herein byreference. This application is a continuation of U.S. patent applicationSer. No. 12/687,025, filed on Jan. 13, 2010, entitled “MINIATUREACTUATOR MECHANISM FOR INTRAVASCULAR IMAGING,” now U.S. Pat. No.8,187,193, which is a continuation of U.S. patent application Ser. No,11/415,855, filed on May 2, 2006, entitled “MINIATURE ACTUATOR MECHANISMFOR INTRAVASCULAR IMAGING,” now U.S. Pat. No. 7,658,715. Thisapplication is also related to U.S. patent application Ser. No.11/415,848, filed on May 2, 2006, entitled “MULTIPLE TRANSDUCERS FORINTRAVASCULAR ULTRASOUND IMAGING” and U.S. patent application Ser. No.11/416,402, filed on May 2, 2006, entitled “MINIATURE ACTUATOR MECHANISMFOR INTRAVASCULAR OPTICAL IMAGING,” the entire contents of each of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a miniature actuator which is useful inintravascular imaging devices including intravascular ultrasound (IVUS),and optical coherence tomography (OCT). The miniature actuator mechanismand ultrasound or OCT imaging device is embedded in an elongate Membersuch as an intravascular guide wire or catheter to provide imagingguidance in various interventional applications. Also disclosed is areflector-based ultrasound imaging device created to minimize theoverall scale of the imaging device, as well as ultrasound transducershaving multiple transducer crystals to increase the field of view of thedevice while maintaining its small size.

2. Description of the Related Art

Coronary artery disease is very serious and often requires an emergencyoperation to save lives. The main cause of coronary artery disease isthe accumulation of plaques inside artery, which eventually occludesblood vessels. Several solutions are available, e.g., balloonangioplasty, rotational atherectomy, and intravascular stents, to openup the clogged section, which is called stenosis. Traditionally, duringthe operation, surgeons rely on X-ray fluoroscopic images that arebasically planary images showing the external shape of the silhouette ofthe lumen of blood vessels. Unfortunately, with X-ray fluoroscopicimages, there is a great deal of uncertainty about the exact extent andorientation of the atherosclerotic lesions responsible for theocclusion, making it difficult to find the exact location of thestenosis. In addition, though it is known that restenosis can occur atthe same place, it is difficult to check the condition inside thevessels after surgery. Similarly, intravascular imaging would provevaluable during interventional procedures as an aid to navigation andfor intraoperative feedback. For example, the precise placement andappropriate expansion of stents would benefit from concurrentintravascular imaging. Existing intravascular imaging devices are toolarge and insufficiently flexible to be placed simultaneously with otherdevices.

In order to resolve these issues, an ultrasonic transducer device hasbeen utilized for endovascular intervention to visualize the inside ofthe blood vessels. To date, the current technology is mostly based onone or more stationary ultrasound transducers or rotating a singletransducer in parallel to the blood vessels by means of a rotating shaftwhich extends through the length of the catheter to a motor or otherrotary device located outside the patient. These devices havelimitations in incorporating other interventional devices into acombination device for therapeutic aspects. They require a large spaceinside catheter such that there is not enough room to accommodate otherinterventional devices. Also due to the nature of the rotating shaft,the distal end of the catheter is very stiff and it is hard to gothrough tortuous arteries. The high speed rotating shaft alsocontributes to distorted non-uniform images when imaging a tortuous pathin the vasculature. OCT has also been utilized to visualize theintravascular space based on differential reflectance, but like theexisting ultrasound devices, most rely on a rotating fiber optic whichextends along the length of the device. This approach also has problems,including for example the manipulation, spinning and scanning motionrequired with respect to a delicate glass or polycarbonate opticalfiber; the actuator mechanism located outside the patient and tiplocated inside the patient are significantly distant from one another,leading to inefficiencies and control issues arising from the torquecreated by a long, spinning member; and remote mechanical manipulationand a long spinning element distort the image due to non-uniformrotational distortion. Given the numerous difficulties with currentintravascular imaging devices, there is a need for improvedintravascular imaging devices.

SUMMARY OF THE INVENTION

One embodiment of the invention is a side-looking intravascularultrasound apparatus comprising an elongate member having a proximal endand a distal end, where at least a portion of the distal end is at leasttransparent to ultrasound energy; an actuator mechanism disposed in thedistal end, the actuator mechanism comprising a first anchor, a secondanchor, at least one movable element, a first SMA actuator connected tothe first anchor and a movable element, and a deformable componentconnected to the second anchor and at least one movable element, wherethe anchor elements are secured relative to the elongate member; and anultrasound transducer connected to the movable element, the transduceroriented to transmit ultrasound energy through the ultrasoundtransparent portion of the distal end at an angle of between about 15°to about 165° relative to a longitudinal axis of the elongate member;where the first SMA actuator has an activated and a deactivated state;and where the movable element and transducer move in a first directionrelative to the elongate member upon activation of the first SMAactuator. In another embodiment of the apparatus, the deformablecomponent comprises a second SMA actuator; where the second actuator hasan activated and a deactivated state; and where activation of the secondSMA actuator following deactivation of the first SMA actuator moves themovable element and transducer relative to the elongate member in asecond direction of movement which is counter to the first direction ofmovement. In yet another embodiment of the apparatus, the deformablecomponent is elastic or superelastic; where the deformable component hasa relaxed state and a deformed state; where the deformable component isin a relaxed state when the first SMA actuator is deactivated; where themovement of the movable element and transducer in the first directionupon activation of the first SMA actuator deforms the elastic orsuperelastic deformable component; and where following deactivation ofthe first SMA actuator, the elastic or superelastic deformable componentsubstantially returns to the relaxed state, the movable element andtransducer moving in a second direction of movement which is counter tothe first direction of movement.

In another embodiment of the apparatus described herein, the first andsecond direction of movement is rotational about the longitudinal axisof the elongate member, or substantially parallel to the longitudinalaxis of the elongate member. In some embodiments, the elongate member isa guide wire. In some embodiments the apparatus further comprises alumen traversing the longitudinal axis of the elongate member; and wiresdisposed in the lumen to electrically connect the transducer, first SMAand optionally the deformable component to one or more devices at theproximal end of the elongate member. In some embodiments the device isan ultrasound signal processor. In some embodiments the apparatusfurther comprises a second ultrasound transducer connected to themovable element. In some embodiments of the apparatus, the angle isbetween about 80° and about 110°; in some embodiments the diameter ofthe distal end of the elongate member is not more than about 0.060inches.

Some embodiments of the apparatus of further comprise a connecting arm,the connecting arm connecting the ultrasound transducer to a movableelement; where the movable element, connecting arm and transducer movein a first direction relative to the elongate member upon activation ofthe first SMA actuator. In some embodiments of the apparatus, thedeformable component comprises a second SMA actuator; where the secondactuator has an activated and a deactivated state; and where activationof the second SMA actuator following deactivation of the first SMAactuator moves the movable element, connector and transducer relative tothe elongate member in a second direction of movement which is counterto the first direction of movement. In some embodiments the deformablecomponent is elastic or superelastic; where the deformable component hasa relaxed state and a deformed state; where the deformable component isin a relaxed state when the first SMA actuator is deactivated; where themovement of the movable element, connecting arm and transducer in thefirst direction upon activation of the first SMA actuator deforms theelastic or superelastic deformable component; and where followingdeactivation of the first SMA actuator, the elastic or superelasticdeformable component substantially returns to the relaxed state, themovable element, connecting arm and transducer moving in a seconddirection of movement which is counter to the first direction ofmovement.

In some embodiments, the rotational motion is between about 1 and about400 degrees, and the longitudinal motion is from about 1 mm to about 20mm. Some embodiments further comprise a second ultrasound transducerconnected to a movable element. In some embodiments, the ultrasoundtransducer further comprises at least two ultrasound crystals. In someembodiments, the transducer is oriented to transmit ultrasound energythrough the ultrasound transparent portion of the distal end at an angleof between about 80° and about 110° relative to a longitudinal axis ofthe elongate member.

Another embodiment is a side-looking intravascular ultrasound apparatuscomprising an elongate member having a proximal end and a distal end,where at least a portion of the distal end is transparent to ultrasoundenergy; an actuator mechanism disposed in the distal end, the actuatormechanism comprising a first anchor, a second anchor, a movable element,a first SMA actuator connected to the first anchor and the movableelement, and a deformable component connected to the second anchor andthe movable element, where the anchor elements are secured relative tothe elongate member; a connecting arm and an ultrasound energyreflector, where the connecting arm connects the ultrasound energyreflector to a moveable element; and an ultrasound transducer disposedin the distal end of the elongate member; where the ultrasoundtransducer and the ultrasound energy reflector are oriented to transmitultrasound energy through the ultrasound transparent portion of thedistal end at an angle of between about 15° to about 165° relative to alongitudinal axis of the elongate member; where the first SMA actuatorhas an activated and a deactivated state; and where the movable element,connecting arm, and ultrasound energy reflector move in a firstdirection relative to the elongate member upon activation of the firstSMA actuator. In some embodiments the deformable component comprises asecond SMA actuator; where the second actuator has an activated and adeactivated state; and where activation of the second SMA actuatorfollowing deactivation of the first SMA moves the movable element,connecting arm and reflector relative to the elongate member in a seconddirection which is counter to the first direction of movement. In someembodiments the deformable component is elastic or superelastic; wherethe deformable component has a relaxed state and a deformed state; wherethe deformable component is in a relaxed state when the first SMAactuator is deactivated; where the movement of the movable element,connecting arm and reflector in the first direction upon activation ofthe first SMA actuator deforms the elastic or superelastic deformablecomponent; and where following deactivation of the first SMA actuator,the elastic or superelastic deformable component substantially returnsto the relaxed state, the movable element, connecting element andreflector moving in a second direction of movement which is counter tothe first direction of movement. Some embodiments further comprise asecond ultrasound energy reflector connected to a movable element. Insome embodiments, the ultrasound transducer and the ultrasound energyreflector are oriented to transmit ultrasound energy through theultrasound transparent portion of the distal end at an angle of betweenabout 80° and about 110° relative to a longitudinal axis of the elongatemember

Also disclosed is a method for visualizing the interior of a patient'svasculature, the method comprising inserting the distal end of anapparatus disclosed herein into the vasculature of a patient; generatingan ultrasound signal from the transducer; generating a cyclical movementof the movable element and ultrasound transducer by alternating theactivation and deactivation of the first SMA and optionally thedeformable component, such that the movable element and ultrasoundtransducer are moved in the first and the second direction; receiving anultrasonic signal reflected from the interior of the vasculature on thetransducer; and producing an image from the reflected signal. In someembodiments of the method, the cyclical movement of the movable elementand ultrasound transducer is generated by alternating the activation ofthe first SMA and the second SMA, such that the movable element andultrasound transducer are moved in the first and the second direction.

Another embodiment of the method for visualizing the interior of apatient's vasculature comprises inserting the distal end of an apparatusdescribed herein into the vasculature of a patient; generating anultrasound signal from the transducer; generating a cyclical movement ofthe movable element, connecting arm and ultrasound transducer byalternating the activation and deactivation of the first SMA andoptionally the deformable component, such that the movable element,connecting arm and ultrasound transducer are moved in the first and thesecond direction; receiving an ultrasonic signal reflected from theinterior of the vasculature on the transducer; and producing an imagefrom the reflected signal. In some embodiments of the method, thecyclical movement of the movable element, connecting arm and ultrasoundtransducer is generated by alternating the activation of the first SMAand the second SMA, such that the movable element, connecting arm andultrasound transducer are moved in the first and the second direction.

Another embodiment of the method for visualizing the interior of apatient's vasculature comprises inserting the distal end of an apparatusdescribed herein into the vasculature of a patient; generating anultrasound signal from the transducer; generating a cyclical movement ofthe movable element, connecting arm and ultrasound energy reflector byalternating the activation of the first SMA and the second SMA, suchthat the movable element, connecting arm and ultrasound energy reflectorare moved in the first and the second direction; receiving an ultrasonicsignal reflected from the interior of the vasculature on the transducer;and producing an image from the reflected signal. In some embodiments,the cyclical movement of the movable element, connecting arm andultrasound energy reflector are generated by alternating the activationof the first SMA and the second SMA, such that the movable element,connecting arm and ultrasound energy reflector are moved in the firstand the second direction.

Another embodiment of the apparatus comprises an elongate member havinga proximal end and a distal end, where at least a portion of the distalend is transparent to ultrasound energy; an ultrasound transducerdisposed in the distal end; and an actuator mechanism means forproviding cyclical motion to the transducer disposed in the distal end;where the transducer is oriented to transmit ultrasound energy throughthe ultrasound transparent portion of the distal end at an angle ofbetween about 15° to about 165° relative to a longitudinal axis of theelongate member. In some embodiments the actuator mechanism meanscomprises a first anchor, a second anchor, a movable element, a firstSMA actuator connected to the first anchor and the movable element, anda deformable component connected to the second anchor and the movableelement, where the anchor elements are secured relative to the elongatemember.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cut-away perspective view showing an embodiment ofthe actuator mechanism of the present invention and an ultrasoundtransducer disposed in the distal end of an elongate member.

FIGS. 2 a and 2 b are perspective views illustrating rotational motionof the actuator mechanism shown in FIG. 1, while FIGS. 2 c and 2 dillustrate longitudinal motion of the actuator mechanism shown in FIG.1.

FIG. 3 is a perspective view showing an embodiment of the actuatormechanism of the present invention connected to an ultrasound transducerby a connecting arm.

FIG. 4 is a perspective view of the device of FIG. 3 disposed in thedistal end of an elongate member having an ultrasound transparentwindow.

FIG. 5 is a perspective view of the distal end of an elongate memberwith an actuator mechanism and ultrasound transducer structure disposedtherein.

FIG. 6 is a perspective view of the distal end of an elongate memberwith an actuator mechanism and two ultrasound support structures stackedorthogonally.

FIG. 7 is a perspective view showing an actuator mechanism with anultrasound reflector connected by a connecting arm, with an ultrasoundtransducer aligned with the reflector.

FIG. 8 is a partial cut-away perspective view showing the device of FIG.7 housed in the distal end of an elongate member with an ultrasoundtransparent window.

FIG. 9 is a schematic drawing of an optical coherence tomography devicewith an actuator mechanism, a reflector and an optical fiber disposed inan elongate member having a transparent window.

FIG. 10 is a schematic drawing of another embodiment of an opticalcoherence tomography device with an actuator mechanism connected to anoptical fiber with a reflector on its distal end, disposed in anelongate member having an transparent window.

FIG. 11 is a schematic drawing of another embodiment of an opticalcoherence tomography device with an actuator mechanism, a reflector andan optical fiber disposed in an elongate member having a transparentwindow.

FIGS. 12 a, 12 b, and 12 c are schematic drawings illustratingultrasound transducers having one, two, or three individual transducercrystals, respectively. FIGS. 12 d, 12 e, and 12 f illustrate the fieldof view obtained by rotating the transducers of FIGS. 12 a, 12 b, and 12c, respectively.

FIGS. 13 a and 13 b are perspective views showing two tubular structureseach with a built-in compliant mechanism in different designconfiguration.

FIG. 14 is a perspective view showing an ultrasound transducer coupledto a micromanipulator having the compliant structure of FIG. 13 a andtwo SMA actuators configured to actuate the compliant mechanism thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to imaging devices for intravascularimaging, although the present invention is not limited to this preferredapplication. Imaging of the intravascular space, particularly theinterior walls of the vasculature can be accomplished by a number ofdifferent means. Two of the most common are the use of ultrasoundenergy, commonly known as intravascular ultrasound (IVUS) and opticalcoherence tomography (OCT). Both of these methods are optimized when theinstruments (IVUS or OCT) used for imaging a particular portion of thevasculature are repeatedly swept over the area being imaged.

To address the limitations in current devices, a new intravascularimaging device is described based on a Shape Memory Alloy (SMA) actuatormechanism embedded inside an elongate member such as a guide wire orcatheter. The present invention utilizes a novel SMA mechanism toprovide side-looking imaging by providing movement for an ultrasoundtransducer or OCT element. Since this novel SMA actuator mechanism canbe easily fabricated in micro-scale using laser machining or otherfabrication techniques, it provides an advantage over existing imagingdevices because it offers the ability to miniaturize the overall size ofthe device, while the use of multiple transducer crystals maximizesfield of view. The small dimensions of the actuator mechanism of theinvention allows for the diameter of the elongate member in which it ishoused to be very small. The outside diameter of the elongate member,such as a guide wire or catheter containing an imaging device describedherein can be as small as from about 0.0050″ to about 0.060″ outsidediameter. The outside diameter for elongate members can be larger whenthe imaging device is combined with other interventional devices,although the outside diameter of these devices can be as small as 0.060″or smaller. Current catheters containing IVUS range from 0.70 mm to 3 mmin outside diameter.

Because the device does not require a rotating shaft or fiber opticalong the length of the catheter, it also allows for a more flexiblecatheter or guide wire, and provides room for other interventionaldevices. In addition, it eliminates the problems mentioned above withcurrent OCT technology because it does not require rotating the entirelength of the optical fiber. This invention simplifies the manufactureand operation of OCT by allowing a straight fiber optic directed by anindependent, oscillating reflector or prism controlled by the actuatormechanism located only in the distal tip of the device. A variation usesthe actuator mechanism to rotate only the distal end of the opticalfiber, eliminating the need to spin the entire fiber via a remotemechanism.

In a preferred embodiment, an ultrasound reflector can be implementedtogether with the SMA actuator mechanism. This has an advantage over theprior art because it eliminates the rotational load required to rotate atransducer and accompanying electrical wiring, further reducing size andincreasing the amount of movement provided by the actuator, which inturn increases the field of view provided by the device. This preferredembodiment also increases imaging quality by allowing for a thickerbacking layer for the ultrasound transducer, since the backing layerdoes not affect the diameter of the device. This in turn improves thesignal-to-noise characteristics of the device and thus improves imagequality. In addition, because the transducer does not need to berotated, this also removes a constraint on the size of the backinglayer.

As used herein, elongate member includes any thin, long, flexiblestructure which can be inserted into the vasculature of a patient.Elongate members include, for example, intravascular catheters and guidewires. The actuator mechanism is disposed in the distal end of theelongate member. As used herein, “distal end” of the elongate memberincludes any portion of the elongate member from the mid-point to thedistal tip. As elongate members can be solid, some will include ahousing portion at the distal end for receiving the actuator mechanism.Such housing portions can be tubular structures attached to the side ofthe distal end or attached to the distal end of the elongate member.Other elongate members are tubular and have one or more lumens in whichthe actuator mechanism can be housed at the distal end.

“Connected” and variations thereof as used herein includes directconnections, such as being glued or otherwise fastened directly to, on,within, etc. another element, as well as indirect connections where oneor more elements are disposed between the connected elements.

“Secured” and variations thereof as used includes methods by which anelement is directly secured to another element, such as being glued orotherwise fastened directly to, on, within, etc. another element, aswell as indirect means of securing two elements together where one ormore elements are disposed between the secured elements.

Movements which are counter are movements in the opposite direction. Forexample, if the movable element is rotated clockwise, rotation in acounterclockwise direction is a movement which is counter to theclockwise rotation Similarly, if the movable element is movedsubstantially parallel to the longitudinal axis of the elongate memberin a distal direction, movement substantially parallel to thelongitudinal axis in a proximal direction is a counter movement.

As used herein, “light” or “light energy” encompasses electromagneticradiation in the wavelength range including infrared, visible,ultraviolet, and X rays. The preferred range of wavelengths for OCT isfrom about 400 nm to about 1400 nm. For intravascular applications, thepreferred wavelength is about 1200 to about 1400 nm. Optical fibersinclude fibers of any material which can be used to transmit lightenergy from one end of the fiber to the other.

“Reflector” as used herein encompasses any material which reflects orrefracts a substantial portion of the ultrasound or light energydirected at it. In some embodiments of the OCT device the reflector is amirror. In others, it is a prism. This allows refractive opticalcoherence tomography (as opposed to reflective tomography using amirror.) The prism can also be designed to replace the lens typicallyrequired at the distal tip of the optical fiber.

Embodiments of the invention will now be described with reference to theaccompanying Figures, wherein like numerals refer to like elementsthroughout. The terminology used in the description presented herein isnot intended to be interpreted in any limited or restrictive manner,simply because it is being utilized in conjunction with a detaileddescription of certain specific embodiments of the invention.Furthermore, embodiments of the invention can include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the inventions hereindescribed.

FIG. 1 illustrates a novel actuator mechanism 10 for achieving thesweeping or scanning motion used for IVUS or OCT imaging. FIG. 1 showsan actuator mechanism 10, which is housed in the distal end of anelongate member 11, with the longitudinal axis of the actuator mechanism10 oriented substantially parallel to the longitudinal axis of theelongate member 11. The elongate member 11 will be described in greaterdetail below with reference to FIG. 4. The actuator mechanism 10includes a first anchor 12 and a second anchor 14 which are securedrelative to the interior of the elongate member 11 to anchor theactuator mechanism 10 to the distal end of elongate member 11 such thatthe anchors 12 and 14 cannot move relative to elongate member 11. Theactuator mechanism 10 also has a movable element 16 which is not securedrelative to the elongate member 11, and which is free to move in atleast one range of motion relative to the anchors 12 and 14 and elongatemember 11.

The first anchor 12 is connected to the movable element 16 by a shapememory alloy (SMA) actuator 20 which moves movable element 16 whenactivated as described in more detail below. The SMA actuator 20 can befabricated from any known material with shape memory characteristics,the preferred material being nitinol. In an alternative embodiment theactuator mechanism 10 can be fabricated without from a single tubingusing any material with shape memory characteristics, incorporating thefirst anchor 12, second anchor 14, moveable element 16, SMA actuator 20and deformable component 22 (described below). As known by those ofskill in the art, SMAs can be fabricated to take on a predeterminedshape when activated. Activation of an SMA actuator consists of heatingthe SMA such that it adopts its trained shape. Typically, this isaccomplished by applying an electric current across the SMA element.Deactivation of an SMA actuator includes turning off current to SMA,such that it returns to its pliable state as it cools. Activation of theSMA to its trained shape results in a force which can be utilized as anactuator. As one of skill in the art will recognize, the disclosed SMAactuator 20 can take numerous shapes and configurations in addition tothe helical shape shown in FIG. 1. For example it could be linear, ormore than one (e.g. 2, 3, 4 or more) SMA elements could be used to makethe SMA actuator 20.

The second anchor 14 is connected to the movable element 16 by adeformable component 22. The deformable component 22 is made frommaterials which are not rigid, including elastic and superelastic, andnon-elastic materials. Deformable materials include trained anduntrained SMAs. Elastic alloys include, but are not limited to stainlesssteel and titanium alloy, and superelastic alloys include but are notlimited to, nitinol, Cu—Al—Ni, Cu—Al, Cu—Zn—Al, Ti—V and Ti—Nb alloy.

In an alternative embodiment, one or both of the anchors 12 and 14 areeliminated, and one end the SMA actuator 20 and/or the deformablecomponent 22 are secured directly to the elongate member 11. Also one orboth of the anchors 12 and 14 are secured indirectly to the elongatemember 11 through additional elements such as an intermediate housingfor the actuator mechanism 10. In addition, the SMA actuator 20 and/ordeformable component 22 can be connected to either of, or both theanchor 12 or 14 and the movable element 16 through additionalelements—they need not be directly connected to the anchor or movableelement as shown. Alternatively, the moveable element 16 can include, orhave an additional element(s) connected thereto, that extend over orwithin the anchors 12 and/or 14 with enough clearance such that theadditional element(s) supports the movement of the moveable element 16and help to align it relative to the anchors 12 and 14—this alignmentprovides precise and uniform motion in the elongate member 11.

In the embodiment illustrated in FIG. 1, an ultrasound transducer 24 isconnected to the movable element of the actuator mechanism by beingdisposed on the moveable element.

In addition, while FIG. 1 shows only a single moveable element, multiplemoveable elements are possible. For example, the SMA actuator 20 couldbe connected to a first moveable element, and the deformable component22 could be connected to a second moveable element, with the transducer24 disposed between the two moveable elements. Alternatively, themoveable element(s) can be eliminated and the SMA actuator 20 and thedeformable component 22 can be attached directly to the ultrasoundtransducer 24.

In the embodiment shown in FIG. 1, the ultrasound transducer 24 isoriented such that it transmits ultrasound energy at an angle of about90° relative to the longitudinal axes of the actuator mechanism 10 andelongate member 11. The angle of orientation of the ultrasoundtransducer 24 relative to the longitudinal axes can be any angle betweenabout 15° and about 165°, with the preferred angle for side-lookingultrasound being between about 80° and about 110°. Angles contemplatedinclude about 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80,85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155,160, and about 165 degrees, or can fall within a range between any twoof these values. For example, 15 (or 165, depending on orientation)degrees are preferred for forward-looking ultrasound imagingapplications.

Housed in the elongate member 11, the actuator 10 shown in FIG. 1 can beused to generate movement of the moveable element 16 as shown in FIG. 2.By activating the SMA actuator 20, a force is generated which displacesthe moveable element 16 and transducer 24 in a first direction since theanchor 12 is secured relative to the elongate member (not shown). FIG. 2a illustrates movement in a first direction, indicated by the arrow,which is rotational about the longitudinal axis of the actuatormechanism 10. FIG. 2 c illustrates a movement in a first direction,indicated by the arrow, which is substantially parallel to thelongitudinal axis of the actuator mechanism 10. The direction ofmovement generated by activation of the SMA actuator 20 will depend onconfiguration of the SMA actuator 20 relative to the anchor 12 andmoveable element 16, as well as the shape which is trained into the SMAactuator 20. For example, the SMA actuator 20 shown in FIG. 2 a istrained to twist when activated, while the SMA actuator 20′ shown inFIG. 2 c is trained to contract. A combination of rotational andlongitudinal movements is possible as well, for example by using an SMAactuator trained to twist and extend or contract, or by using acombination of SMA elements or actuators. For example, two or more SMAactuators could be linked in series.

FIGS. 2 b and 2 d illustrate counter movements in a second direction,indicated by the arrows, which provides an oscillating movement to themoveable element 16 and transducer 24. This counter movement is providedby the deformable component 22 or 22′, preferably when the SMA actuator20 or 20′ is deactivated. The deformable component 22 can be any elasticor superelastic material, or a second SMA actuator. The deformablecomponent is in a relaxed state when the SMA actuator 20 or 20′ is inthe deactivated state. When the first SMA actuator 20 or 20′ isactivated, as shown in FIGS. 2 a and 2 c, the deformable component 22 or22′ is deformed by the movement of the moveable element 16 since thesecond anchor 14 is secured relative to the elongate member (not shown).

In an embodiment where the deformable component 22 or 22′ is an elasticor superelastic material, the energy stored in the deformable component22 or 22′ when it is in its deformed state shown in FIGS. 2 a and 2 cmoves the moveable element 16 and transducer 24 to the position shown inFIGS. 2 b and 2 d when the first SMA 20 or 20′ is deactivated. Thismovement in the second direction, indicated by the arrow, is counter tothe movement in the first direction. By alternately activating anddeactivating the first SMA 20 or 20′, a cyclical movement of themoveable element 16 and transducer 24 will result. This cyclicalmovement can be rotational about the longitudinal axis of the of theactuator mechanism 10 as shown in FIGS. 2 a and 2 b, or approximatelyparallel to the longitudinal axis of the actuator mechanism 10 as shownin FIGS. 2 c and 2 d, or a combination of rotational and longitudinalmovement (not shown).

In a preferred embodiment, the deformable component 22 or 22′ is asecond SMA actuator that is trained to move the moveable element 16 andtransducer 24 in a second direction which is counter the movement in thefirst direction caused by activation of the first SMA actuator 20 or20′. In this embodiment, the cyclical motion is generated by thealternating activation of the first SMA actuator 20 or 20′ and thesecond SMA actuator 22 or 22′. The activation of the first SMA actuator20 or 20′ deforms the second SMA actuator 22 or 22′ which is in itsinactive state, as illustrated in FIGS. 2 a and 2 c. The first SMAactuator 20 or 20′ is deactivated and the second actuator SMA 22 or 22′is activated, causing the deformation of the first SMA actuator 20 or20′ and the movement of the moveable element 16 and transducer 24 asillustrated in FIGS. 2 b and 2 d.

FIG. 3 shows another embodiment of the invention including the actuatormechanism 10 illustrated in FIGS. 1 and 2. As in FIG. 1, the actuatormechanism 10 in FIG. 3 includes a first anchor 12, a second anchor 14, amovable element 16. The first anchor 12 is connected to the movableelement 16 by a SMA actuator 20. The second anchor 14 is connected tothe movable element 16 by a deformable component 22. In the embodimentillustrated in FIG. 3, the ultrasound transducer 24 is connected to themoveable element 16 by a connecting arm 26, such that movement of themoveable element 16 results in movement of the ultrasound transducer 24and connecting arm 26. The movement of the moveable element 16 isgenerated as described above and illustrated in FIG. 2. In an alternateembodiment, the portion of the connecting arm 26 that is shown extendingpast the moveable element 16 and passing through the second anchor 14 isremoved. The connecting arm 26 can have a lumen (not shown), andoptionally wires can pass through the lumen to connect the transducer 24to an ultrasound signal generator and processor located at the proximalend of the elongate member in which the actuator mechanism andtransducer are housed. While the actuator mechanism 10 is illustrated ashaving the SMA actuator 20 in closer proximity to the transducer 24 thanthe deformable component 22, one of skill in the art will readilyappreciate that the actuator mechanism 10 can be oriented such that thelocation of the SMA actuator 20 and the deformable component 22 arereversed.

In several embodiments disclosed herein, the connecting arm 26 is shownpassing through the center of the anchor 12 and 14 and moveable element16. One of skill in the art will recognize that it is not necessary tolocate the connecting arm 26 along the longitudinal axis of the actuatormechanism 10. For example, the connecting arm 26 could be located on anexterior surface of the moveable element 16, and the anchor 12 couldhave a cut-out to allow the movement of the connecting arm 26 over theanchor 12. In addition, it can be desirable to provide structuralsupports for the moveable element 16 to stabilize its movement withinthe elongate member.

FIG. 4 illustrates an elongate member 30 which has a distal end 32 inwhich the actuator mechanism and ultrasound transducer 34 are housed.The distal end 32 of the elongate member 30 has at least a portion 36 ofthe elongate member which is transparent to ultrasound energy. Theultrasound transducer 34 is oriented to transmit and receive ultrasoundenergy through this portion 36. The ultrasound transparent portion 36can be a window made of an ultrasound transparent material, a materialwhich is partially or substantially transparent to ultrasound energy, orthe window can be a cut-out such that there is no material between thetransducer and the outside environment. The portion 36 is desirablewhere the distal end 32 of the elongate member 30 is made of a substancethat absorbs ultrasound energy. In an alternative embodiment, the entiredistal end 32 or elongate member 30 is transparent to ultrasound energy.

FIG. 5 illustrates the distal end 40 of an elongate member, where allbut the distal tip 41 of the elongate member is transparent so that theactuator mechanism 42 housed in the distal end 40 is visible. Theactuator mechanism 42 is similar to the one illustrated in FIG. 3, withthe addition of support members 44 disposed within the anchors 46. Thesupport members 44 support the connecting arm 50, which connects themoveable element 52 and ultrasound transducer structure 54, acting tostabilize the movements of the connecting arm 50 and moveable element52. The connecting arm 50 is free to rotate or slide within the supportmembers 44, but not the moveable element 52. The support members 44 canbe separate elements as shown in FIG. 5, or the anchors 46 can befabricated to perform the function of the support members 44. Theactuator mechanism 42 is used to generate movement of the moveableelement 52, connecting arm 50 and ultrasound transducer structure 54 inthe manner described above in reference to FIG. 2. The connecting arm 50and moveable element 52 can be a single piece. In another embodiment,the moveable element 52 is eliminated, and the SMA actuator 62 anddeformable component 64 are attached directly to the connecting arm 50.

In the embodiment shown in FIG. 5, the ultrasound transducer structure54 has two ultrasound transducer crystals 56 and 56′ for sending andreceiving the ultrasound signal, which share a common backing 60. Thebacking 60 provides support for the transducer crystals 56 and 56′, aswell as a barrier to absorb the ultrasound energy emitted by the backface of the transducer crystals 56 and 56′. By using two transducercrystals 56 and 56′, more of the interior wall of the vasculature orother structure can be imaged by a device of approximately the samesize.

FIG. 6 shows another embodiment wherein there are two ultrasound supportstructures 70 and 70′ stacked orthogonally, with each transducer supportstructure 70 and 70′ having two transducer crystals 72 and 72′ sharing acommon backing 74 and 74′. This configuration allows for an even largerfield of view, as each transducer crystal 72 and 72′ generates a signaloriented in a different direction. One of skill in the art willrecognize that the ultrasound support structures 70 and 70′ can beoriented to each other at any desirable angle. Additionally, thetransducer crystals 72 and 72′ can be oriented on the support structures70 and 70′ and with respect to each other in alternate configurations.Preferred embodiments of ultrasound transducers having more than onetransducer crystal are described in more detail below and in referenceto FIG. 12.

FIG. 7 illustrates a preferred embodiment of the current invention.Shown in FIG. 7 is an actuator mechanism 80 which has two anchors 82 and82′, a moveable element 84 connected to the anchor 82 and 82′ by an SMAactuator 86 and a deformable component 90. A connecting arm 92 connectsthe moveable element 84 to an ultrasound energy reflector 94. Thereflector 94 has a surface 96 which is oriented to reflect ultrasoundenergy to and from an ultrasound transducer 100. Movement of themoveable element 84, connecting arm 92 and reflector 94 can be achievedas described above, with reference to FIG. 2. In another embodiment, theactuator mechanism 80 is configured to move the reflector 94substantially parallel to the longitudinal axis of the actuatormechanism 80, as described above. One of skill in the art will recognizethat to maximize longitudinal movement, a space can be introducedbetween the anchor 82′ and the ultrasound energy reflector 94 to allowthe reflector 94 to move in a proximal and distal direction, Asdiscussed above, the orientation of the actuator mechanism 80 could bereversed such that SMA actuator 86 is closer to the reflector 94, andthe deformable component 86 is more distant.

In the embodiment shown in FIG. 7, the transducer 100 and reflector 94are oriented such that ultrasound energy is reflected from thetransducer away from the device at an orthogonal angle, about 90°,relative to the longitudinal axes of the actuator mechanism 80 andelongate member (not shown). The angle of the reflector can be changedso that the ultrasound energy transmitted to and from the ultrasoundtransducer is at an angle between about between about 15° and about165°, with the preferred angle for side-looking ultrasound being betweenabout 80° and about 110°. Angles contemplated include about 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110,115, 120, 125, 130, 135, 140, 145, 150, 155, 160, and about 165 degrees,or can fall within a range between any two of these values. Bydecreasing the angle between the surface of the reflector and thesurface of the transducer, the ultrasound energy will be reflected in amore forward-looking direction, that is toward the distal tip of thedevice. This can be useful in some applications where it is desirable toimage the area in front of the device, such as when navigating atortuous path through a blockage in the vasculature.

In the embodiment shown in FIG. 7, the reflector 94 can be shaped forspecific purposes. For example, the surface 96 can be concave to focusthe ultrasound beam into a smaller beam for certain imagingrequirements. In other embodiments the surface is convex. In otherembodiments, the reflector 94 has more than one reflective surface.

FIG. 8 is a partial cut-away view which illustrates the device of FIG. 7housed in the distal end 102 of an elongate member. A portion of thedistal end housing the actuator mechanism 80 is cut away to show theactuator mechanism 80. The portion of the distal end adjacent to thereflector 94 is a window 104 which is transparent to ultrasound energy.This permits ultrasound energy to be transmitted to and from theultrasound transducer 100 through the distal end 102 of the elongatemember. Alternatively, the configuration of the actuator mechanism 80and the transducer 100 can be reversed—the actuator mechanism 80 ishoused in the distal end of the elongate member and the transducer islocated closer to the proximal end of the device.

FIG. 9 is a schematic diagram of another embodiment of the currentinvention, where the imaging apparatus uses optical coherencetomography. OCT relies on light emitted from a fiber optic which isdirected to the surface of the vasculature being imaged. The imagedsurface reflects light back to the device where the same or anotherfiber optic transmits the signal to a processor outside the patient.Based on differential reflectance of the surface, and image is formedfrom the signal. FIG. 9 illustrates an actuator mechanism 110 similar tothe ones disclosed in the previous figures, which has two anchors 112and 112′, a moveable element 114 connected to the anchors 112 and 112′by an SMA actuator 116 and a deformable component 120. A connecting arm122 connects the moveable element 114 to a reflector 124. The reflectorhas a surface 126 which is oriented to reflect light energy to and froman optical fiber 130. The actuator mechanism 110, connecting arm 122,reflector 124 and fiber optic 130 are advantageously housed in thedistal end of an elongate member 132. The apparatus further includes awindow 134 that is transparent to light energy, located at the distalend of the elongate member 132.

While the connecting arm 122 is free to move relative to the anchors 112and 112′, it is secured to the moveable element 114. Movement of themoveable element 114, connecting arm 122 and reflector 124 can beachieved as described above with reference to FIG. 2. Rotationalmovement of the reflector 124 about the longitudinal axes of theactuator mechanism 110 and elongate member 132 is illustrated by thearrow in FIG. 9. In another embodiment, the actuator mechanism 110 isconfigured to move the reflector 124 substantially parallel to thelongitudinal axes, as previously described. Also as discussed above, theconnecting arm 122 can be supported by the anchors 112 and 112′ orsupport elements disposed in the anchors. One of skill in the art willrecognize that the connecting arm 122 and moveable element 114 can befabricated from a single piece of material, or be separate piecessecured together, for example by glue, welding, snap-fit, or frictionalforces due to a tight fit. These are examples only, and are notlimiting. In an alternative embodiment, the SMA actuator 116 anddeformable component 120 are attached directly to the connecting arm122.

Since the optical fiber 130 is stationary and not mounted on theactuator mechanism 110, it eliminates the rotational load associatedwith conventional OCT devices which require rotating the entire lengthof the optical fiber. As a result, the actuator mechanism canpotentially generate a wider range of motion due to the smaller loadassociated with the connecting arm 122 and reflector 124. Since the OCTimaging device is based on a sweeping reflector, the fiber optic is canremain motionless, reducing or eliminating image distortion and issuesassociated with the torque generated by the spinning optical fiber.

The reflector 124 can be shaped for specific purposes. For example, thesurface 126 can be concave to focus the coherent light into a smallerbeam for certain imaging requirements. In other embodiments the surfaceis convex. The surface 126 can be designed to replace the lens typicallyattached to the end of a fiber optic when used for OCT. In this case thereflector 124 is used to focus the coherent light at the distance neededto image the vasculature, and the lens is not necessary. In someembodiments the reflector 124 is a mirror, in others, it is a prism. Aprism allows refractive optical coherence tomography (as opposed toreflective tomography using a mirror.) The prism can also be designed toreplace the lens typically required at the distal tip of the opticalfiber. In other embodiments, the reflector 124 has more than onereflective surface. In another embodiment, one or more additionaloptical fibers and/or reflectors are provided to increase the field ofview, or to provide different wavelengths of light.

FIG. 10 is a schematic of another embodiment of the invention where theactuator mechanism 140 rotates the distal end of the fiber optic usedfor OCT. FIG. 10 illustrates an actuator mechanism 140 which has twoanchors 142 and 142′, a moveable element 144 connected to the anchors142 and 142′ by an SMA actuator 146 and a deformable component 150. Themoveable element 144 is secured to the distal end of a fiber optic 154by, for example but not limited to, crimping, glue, welding, snap-fit,set screw, or frictional forces due to a tight fit. The optical fiber154 which has a prism 156 or other reflective surface mounted on itsdistal tip. The prism 156 has a surface oriented to refract light energyto and from the optical fiber 154 as illustrated by the arrows. Theactuator mechanism 140, fiber optic 154 and prism 156 are shown housedin the distal end of an elongate member 160. In the embodiment shown inFIG. 10, a portion of the distal end of the elongate member is a window162 that is transparent to light energy.

While the optical fiber 154 is free to move relative to the anchors 142and 142′, it is secured to the moveable element 144. Movement of themoveable element 144 can be achieved as described above, and asillustrated in FIG. 2. Because the moveable element 144 is secured tothe fiber optic 154, rotational movement of the moveable element asillustrated by the arrow in FIG. 10 results in rotational movement ofthe distal end of the fiber optic 154 and prism 156 about thelongitudinal axis of the elongate member.

The sweeping motion of the actuator mechanism 140 creates a scanningpattern and can achieve a field of views in a range of angles, dependingupon the strain characteristics of the optical fiber 154. This producesthe required scanning motion for OCT imaging without requiring therotation of the entire fiber optic and the high-speed mechanical rotatorin the proximal end of the device. In another embodiment, one or moreadditional actuator mechanisms are spaced along the fiber optic from thedistal end toward the proximal end, increasing the rotationaldisplacement of the distal end or the entire length of the opticalfiber, and distributing the rotational load generated along the lengthof the optical fiber.

FIG. 11 is a schematic illustration of an actuator mechanism 170, whichhas two anchors 172 and 172′, a moveable element 174 connected to theanchors 172 and 172′ by an SMA actuator 176 and a deformable component180. A reflector 182 is mounted on the moveable element 174. Thereflector has a surface 184 which is oriented to reflect light energy toand from an optical fiber 186. An optional support structure 190stabilizes the moveable element 174. The actuator mechanism 170,reflector 182 and fiber optic 186 are shown housed in the distal end ofan elongate member 192 as shown in FIG. 9. The actuator mechanismprovides cyclical movement of the moveable element 174 and reflector 182as described previously.

FIGS. 9, 10 and 11 illustrate a reflector or prism oriented such thatlight energy is reflected from the fiber optic away from the device atan orthogonal angle, about 90°, relative to the longitudinal axes of theactuator mechanism and elongate member. The angle of the reflector canbe changed so that the light energy transmitted to and from the fiberoptic is at an angle between about 15° and about 165° relative to thelongitudinal axis of the device, with the preferred angle being betweenabout 80° and about 110°. Angles contemplated include about 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110,115, 120, 125, 130, 135, 140, 145, 150, 155, 160, and about 165 degrees,or can fall within a range between any two of these values. By adjustingthe angle between the reflective surface of the reflector or prism andthe end of the fiber optic, the light can be reflected in a moreforward-looking direction, that is toward the distal tip of the device.This can be useful in some applications where it is desirable to imagethe area in front of the device, such as when navigating a tortuous paththrough a blockage in the vasculature.

As described herein, at least a portion of the elongate member istransparent to ultrasound energy or light energy. This includes a windowmade of an ultrasound or light energy transparent material, a materialwhich is partially or substantially transparent to ultrasound or lightenergy, or the window can be a cut-out such that there is no materialbetween the transducer, reflector or prism and the outside environment.En other embodiments the entire distal end or elongate member istransparent.

The actuator described herein can be made very small, such that theactuator has a diameter/width between about 5 μm and about 1000 μm, withthe preferred size being between about 5 μm and about 100 μm. Theactuator preferably has a diameter or width of, or of about, 5, 10, 20,30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900,or 1000 μm, or is at least about, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90,100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 μm, or is no morethan about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400,500, 600, 700, 800, 900, or 1000 μM, or can fall within a range betweenany two of these values. The range of lengths preferred for the actuatoris quite broad, and depends on the application. For rotational motion,the length of the actuator mechanism can be from about 20 μm to about 10mm, with the preferred size being from about 200 μm to about 10 mm. Forlongitudinal motion, the length of the actuator can be from about 100 μmto about 20 mm, with the preferred length being from about 1 mm to about20 mm. The actuator preferably has a length of, or of about, 20, 30, 40,50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900 μm, 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20mm, or is at least about, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300,400, 500, 600, 700, 800, 900 μm, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, or 20 mm, or is no more than about 20, 30,40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900 μm,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20mm, or can fall within a range between any two of these values.

The outside diameter of the elongate member, such as a guide wire orcatheter containing an imaging device described herein can be as smallas from about 0.005″ to about 0.100″ outside diameter. Preferably, theoutside diameter of the elongate member is, or is about 0.5, 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 hundredths of aninch, or is at least about, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, or 100 hundredths of an inch, or is no more thanabout 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95,or 100 hundredths of an inch, or can fall within a range between any twoof these values.

The range of motion generated by the actuator mechanism described hereinwill vary depending of the application. Rotational motion can be in arange from about 1 or 2 degrees up to about 400 degrees, depending onthe area of interest. Angles of rotational displacement generated by theactuator mechanism are, or are about, 1, 2, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120,125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 190, 195,200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265,270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335,340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395, or 400degrees, or at least about 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130,135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 190, 195, 200, 205,210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275,280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345,350, 355, 360, 365, 370, 375, 380, 385, 390, 395, or 400 degrees; or nomore than 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145,150, 155, 160, 165, 170, 175, 180, 190, 195, 200, 205, 210, 215, 220,225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290,295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, 355, 360,365, 370, 375, 380, 385, 390, 395, or 400 degrees, or can fall within arange between any two of these values. By adjusting the power and/orduration of the activation signal to one or more of the SMA actuators,the degree of rotation or length of longitudinal displacement can beadjusted while the device is in the patient, allowing the operator toadjustably define a specific image field of view. The preferred range ofrotational displacement generated by the actuator device is from about25 to 360 degrees. In addition, it is possible to use the device of theinvention for singe point interrogation for optical coherencereflectometry or Doppler effect measurements.

The amount of longitudinal displacement generated by the actuatormechanism is also dependent on the length of the area of interest. Thelength of longitudinal displacement can be from about 100 μm to about 30mm or more. The length of longitudinal displacement generated by theactuator mechanism preferably is, or is about 100, 200, 300, 400, 500,600, 700, 800, 900 μm, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 25, or 30 mm, or is at least about, 100, 200,300, 400, 500, 600, 700, 800, 900 μm, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 25, or 30 mm, or is no more thanabout 100, 200, 300, 400, 500, 600, 700, 800, 900 μm, 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, or 30 mm, orcan fall within a range between any two of these values.

The frequency of the motion generated by the actuator mechanism canrange from about 1 Hz to about 100 Hz. The preferred frequency of motionis between about 8 Hz and 30 Hz. The frequency of movement generated bythe actuator mechanism is, or is about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60,65, 70, 75, 80, 85, 90, 95, or 100 Hz, or at least about 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 Hz, or no more thanabout 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100Hz, or can fall within a range between any two of these values.

In some embodiments, the actuator mechanism disclosed herein is madewithout any mechanical joints.

When the actuator described above is used to generate movement of anultrasound transducer, the area imaged by a single transducer is limitedby the range of movement the actuator can generate. One way to achieve alarger field of view is to use multiple transducer crystals. The priorart discloses phased array devices where individual crystal transducersare used in combination to generate an ultrasound wave for imaging. Inthese prior art devices, the individual crystals are mounted on separatebackings and are not capable of individually producing an ultrasoundsignal for imaging. In contrast, the individual transducer crystals usedin the transducers of the instant are preferably mounted on a sharedbacking and are preferably capable of individually producing anultrasound signal for imaging.

As used herein, transducer crystal or crystal transducer refers to thematerial used to produce and/or receive the ultrasound signal. Materialsused for making the transducer crystal are known in the art and includequartz and ceramics such as barium titanate or lead zirconate titanate.Ultrasound transducer crystals for IVUS utilize frequencies from about 5MHz to about 60 MHz, with the preferred range being from about 20 MHz toabout 45 MHz.

Ultrasound crystals are preferably substantially rectangular, square,elliptical, or circular, although any shape that produces a functionalultrasound transducer is contemplated. As used herein, the top andbottom edge of a transducer crystal are defined by substantiallyparallel lines bounding the transducer, a first and second side edge aredefined by a second set of substantially parallel lines bounding thetransducer, where the lines defining the top and bottom edges aresubstantially perpendicular to the lines defining the first and secondside edges. As defined herein, ellipses, circles, irregular shapes, etc.can have top, bottom, first and second edges.

FIG. 12 illustrates a schematic of ultrasound transducers having one,two or three crystal transducers. The dashed lines shown in FIG. 12represent the direction the ultrasound energy is transmitted andreceived from the transducer crystals. FIG. 12 a shows an ultrasoundtransducer 200 having one crystal transducer 202 on a backing structure204. The backing material can be any material known to those in the artwhich absorbs ultrasound energy radiated from the transducer crystalsback face. FIG. 12 b shows an ultrasound transducer 210 having twocrystal transducers 212 and 214 on a single backing structure 216. FIG.12 c shows an ultrasound transducer 220 having three crystal transducers222, 224 and 226 on a single backing structure 228.

FIGS. 12 d, 12 e, and 12 f show the range of fields of view with thedifferent configurations of transducers shown in FIGS. 12 a, 12 b and 12c, respectively. As an example, assume that the actuator mechanism (notshown) used to move the transducer can generate 60° rotational motion.With a single transducer as shown in FIG. 12 a, rotation of theultrasound transducer 200 through 60° will provide a 60° field of viewas shown in FIG. 12 d, where the crystal transducer 202 is shown at thetwo extremes of the range of motion (the backing 204 is excluded forclarity.) If two transducers 212 and 214 are arranged with a 60° anglebetween their respective fields of view as shown in FIG. 12 b, rotatingthe transducer structure 210 through 60° as shown by the two positionsillustrated in FIG. 12 e will provide a field of view totaling 120° withthe same actuator. Similarly, three-transducers configured with a 60°angle between each crystal transducer 222, 224 and 226 as shown in FIG.12 c will have a field of view equivalent to 180° if the transducer isrotated through 60° as shown in FIG. 12 f.

Although a 60° angle between the beams of the transducer crystals isshown in FIG. 12, any angle between 0° (equivalent to the field of viewprovided by a large crystal) and 180° is encompassed by the presentinvention. Angles encompassed by the invention include about 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100,105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170,175, and about 180 degrees, or can fall within a range between any twoof these values. In some embodiments, the angles defined by the adjacentpairs of crystals are not equal. For example, where three crystals areused, the angle defined by the third crystal and the second crystal canbe different than the angle defined by the first crystal and the secondcrystal. The angle between the faces of the transducer crystals ispreferably about the same as the degrees of deflection which can beachieved by the actuator mechanism. This maximizes field of view withoutsignificant overlap or gaps between the individual fields of view foreach transducer crystal. For example, if two crystal transducers 212 and214 are aligned at 60° as illustrated in FIG. 12 b, but the actuator canonly rotate the transducer structure by 30°, there will be a gap ofapproximately 30° between the fields of view generated by eachtransducer crystal. Similarly, if the actuator can rotate through 90°,there will be a 30° field of view overlap between the two fields of viewgenerated by each transducer crystal. While an overlap or gap in thefields of view can be desirable in some applications, the preferredembodiment provides for minimal gaps or overlaps. Importantly, theindividual transducer crystals are placed with their edges adjacent ortouching, such that the size of any gap between the fields of view ofthe individual crystal transducers is minimized and significantlyreduced. In a preferred embodiment, the individual transducer crystalsare configured such that any gap between the individual fields of vieware substantially eliminated. This provides an improved image quality.

While FIG. 12 illustrates an ultrasound transducer with 1, 2, or 3crystals, more crystals can be used. Also contemplated are ultrasoundtransducers with 4, 5, 6, 7, 8, 9, or 10 transducer crystals. Thecrystals can be arranged on a single backing device, or on multiplebacking devices as illustrated in FIG. 6. For single crystal transducersthe diameter of the crystal if circular shaped, or width if rectangularshaped, is preferably from about 10 μm to about 10 mm, and morepreferably from about 100 μm to about 1 mm. For transducers withmultiple crystals, the combined diameter or width of the individualcrystals is preferably from about 10 μm to about 10 mm, and morepreferably from about 100 μm to about 1 mm. Preferably, the diameter orwidth of the individual crystals on a given transducer is approximatelyequal, although crystals of different diameters or widths can becombined. The individual transducer crystals preferably have a diameteror width of, or of about, 100, 200, 300, 400, 500, 600, 700, 800, 900,or 1000 μm, or are at least about, 100, 200, 300, 400, 500, 600, 700,800, 900, or 1000 μm, or are no more than about 100, 200, 300, 400, 500,600, 700, 800, 900, or 1000 μm, or can fall within a range between anytwo of these values.

In another embodiment, the multiple transducer configurations disclosedherein are utilized in a device in which the actuator is configured toprovide longitudinal, rather than rotational motion, for example asshown in FIGS. 2 c and 2 d. As with the rotational movement illustratedin FIG. 12, combining multiple transducers with longitudinal motion canalso provide a larger field of view with the same actuator.

The multiple transducer configuration disclosed herein can also be usedfor forward looking ultrasound devices. Providing a 180° field of viewallows ultrasound imaging with the capability of side-looking as well asforward-looking in a single device. A preferred forward looking deviceis disclosed in U.S. Patent Publication No. US-2004-0056751-A1, which isherein incorporated by reference in its entirety. Other forward lookingdevices include those disclosed in U.S. Pat. Nos. 5,379,772 and5,377,685, which are herein incorporated by reference. As used herein, apivot point is a point around which the transducer is rotated, andincludes mechanical joints, for example those disclosed in U.S. Pat. No.5,379,772, FIGS. 2, 5, and 6. While the aforementioned forward lookingdevices disclose a single crystal transducer, applicants have discoveredthat transducers having multiple crystals dramatically increase thefield of view. As was described with reference to side-looking devices,the multiple crystal transducers are disposed on the actuator mechanism.

U.S. Patent Publication No. US-2004-0056751-A1 discloses an elastic orsuperelastic material utilized as a structural material for amicromanipulator. In principle, when a compliant mechanism is deformedwith an actuator, strain energy is stored inside the underlyingstructure during deformation (elastic and plastic). The stored energy isthen directly utilized to produce a bias force to return the structureto its original shape. However, an elastic material such as stainlesssteel can also be utilized as a structural material for compliantmechanisms.

According to an aspect of the disclosure, a Nd:YAG laser is implementedin the fabrication of the compliant structure out of a tube. A tubularnitinol structure with compliant mechanism was successfully fabricatedusing laser machining with a laser beam size of about 30 μm. The outerdiameter of the tube is about 800 μm and the wall thickness is about 75μm. Actual feature size is about 25 μm, which is mostly limited by thesize of the laser beam. Thus, by reducing the beam size, resolution ofthe laser machining can be enhanced.

To shape a nitinol structure, there are three fabrication processescurrently commercially available: chemical etching, laser machining andmicro-mechanical cutting. However, these two processes are not able toprecisely control etching depth. Thus, it is very difficult to have avariation in thickness and, consequently, the thickness of the mechanismdetermines the substrate thickness. This presents another issue indesign, which is structural rigidity. For instance, if the substratethickness is on the order of tens of microns, the supporting structurealso starts deflecting as the mechanism moves. This deflection at thesupporting structure, which is supposed to be fixed, directlycontributes to loss of output displacement. Structural rigidity ismostly a shape factor, which is related to flexural modulus, EI.Considering the structural rigidity, a tube shape is more attractivethan a plate form.

FIG. 13 a illustrates an exemplary tubular structure 1200 a with abuilt-in compliant mechanism 1201 a. FIG. 13 b illustrates anotherexemplary tubular structure 1200 b with a built-in compliant mechanism1201 b in a helical configuration having helix 1291 and helix 1292intertwined in a “double helix”-like fashion. The mechanism design canbe any shape and/or configuration as long as it utilizes structuralcompliance (elasticity and/or superelasticity) as a main designparameter. Similarly, as one skilled in the art would appreciate, therest of the tubular structure can be in any suitable configuration,size, and length, etc., optimized for a particular application and thusis not limited to what is shown here. Moreover, in addition to nitinol,other flexible, resilient biocompatible metal or polymer materials canalso be utilized as long as they have reversible structural behaviors,i.e., have elastic and/or superelastic behaviors while actuated.

As illustrated in FIG. 13 b, compliant mechanisms can be in a “doublehelix” configuration. U.S. Patent Publication No. US-2004-0056751-A1teaches that it is desirable with the disclosed invention that anybending strain of the compliant mechanisms is distributed substantiallyevenly along their entire lengths. This reduces peak strain, which invarious embodiments, can be, 4% or less, 3% or less, 2% or less and 1%or less. The “double helix” configuration provides greater symmetry inmotion and provides a more even bending It is desired that the stiffnessof compliant mechanisms in different directions be substantially thesame.

In various embodiments, the elastic bending strength of the compliantmechanisms is customized in order to match with that of the actuators.In some embodiments, the actuators have slightly stiffer elastic bendingstrengths than those of the compliant mechanisms. In one embodiment, thecompliant mechanisms are stiffer than the actuators when the actuatorsare relaxed, and the compliant mechanisms are softer than the actuatorswhen the actuators are active. It is desirable to provide compliantmechanisms in configurations, such as those of the “double helix”configurations, that have as little stress concentration as possible.

According to the invention disclosed in U.S. Patent Publication No.US-2004-0056751-A1, the strain of a compliant mechanism is distributed,while minimizing the occurrence of strain location. The mechanicalcharacterization of a compliant mechanism can be tuned by modificationsin, (i) stiffness, (ii) peak strain (maximum strain), (iii) size, (iv)fatigue life, and the like. In one embodiment, the upper limit of strainis no more than 4%. The bending stiffness depends on actual application.By way of illustration, and without limitation, the bending stiffness ofa compliant mechanism can be at least 0.5 N-mm and no more than 10 N-mm.In various embodiments, compliant mechanisms are stiffer than theimaging device. The associated actuators are also stiffer than theimaging device. The actuators need a longer thermal time constant thanthe imagining device.

FIG. 14 schematically shows, according to an aspect of the inventiondisclosed in U.S. Patent Publication No. US-2004-0056751-A1, amicromanipulator 1300 tightly coupled with an ultrasound transducer 1310for image scanning. Micromanipulator 1300, as well as the otherembodiments of micromanipulators disclosed herein, provide for steering,viewing and treatment at sites within vessels of the body, as well asfor industrial applications.

The micromanipulator 1300 enables the ultrasound transducer 1310 to bedirectly coupled to the compliant mechanisms 1301. In this fashion, therotational center of the transducer 1310 for the scanning motion issubstantially closer to the rotational axis of the mechanism 1301. In anembodiment, SMAs are implemented as main actuators 1320 for themicromanipulator 1300. To allow the SMAs 1320 be attached thereto, themicromanipulator 1300 might have one or more attachment points orbuilt-in micro structures such as welding-enabling structures 1302 asshown in a cross-sectional view A-A and clamping-enabling structures1302′ as shown in another cross-sectional view A′-A′. In someembodiments, the SMAs 1320 are attached to the compliant apparatus viathe one or more attachment points or welding-enabling structure 1302using a laser having a laser beam size of about 200 μm or less. In someembodiments, the SMAs 1320 are fastened to the compliant apparatus viathe built-in clamping-enabling structures 1302′.

The compliant mechanisms 1301 are actuated with SMA 1320 actuators basedon shape memory effects including contraction as well as rotation motionto maximize output displacement. As one skilled in the art canappreciate, the SMA actuators can be in any shape such as wire, spring,coil, etc. and thus is not limited to what is shown.

Another aspect of the current invention is a method for visualizing theinterior of a patient's vasculature, or other structure with a lumen.The method comprises inserting the inserting the distal end of theelongate member of any of the apparatuses disclosed herein into thevasculature of a patient. The distal end is advanced through thevasculature, optionally under the guidance of x-ray fluoroscopic imagingto the location of the blockage, legion, or other area to be imaged.Alternatively, the imaging device can be used instead of or in additionto the x-ray fluoroscopic imaging to guide the device through thevasculature.

To generate an image, an ultrasound signal generator/processor locatedoutside the patient is activated, generating an ultrasound signal fromthe ultrasound transducer. The actuator mechanism described herein isused to generate a cyclical movement of the ultrasound transducer orreflector as described above. In the case of OCT, the fiber optic isused to transmit a light signal from a signal processor unit outside thepatient to the distal tip of the optical fiber. The reflector, prism, ordistal end of the optical fiber is moved in a cyclical motion by theactuator mechanism as described herein. The cyclical movement sweeps theultrasound or light energy over the area being imaged. The ultrasound orlight energy is reflected back to the ultrasound transducer or fiberoptic, respectively. The signal is then transmitted to the proximal endof the device where it is processed to produce an image.

In some embodiments of the current invention, the elongate member hasone or more lumens along the longitudinal axis of the elongate member.The lumen(s) can be used to house the actuator mechanism, compliantmechanism, optical fiber and other devices described herein. Thelumen(s) can also be used to house wiring which connects the ultrasoundtransducer(s) and SMA actuator(s) disposed in the distal end of theelongate member to devices located adjacent to the proximal end of theelongate member. These devices include, for example, other components ofan ultrasound or OCT imaging system, such as an ultrasound or lightsource generator, receiver and computer located near the proximal end ofthe elongate member. In some embodiments, the imaging device of theinvention is connected wirelessly to one or more components of theimaging system. The ultrasound imaging device of the invention isoptionally configured to provide real-time imaging of the environment atthe distal end of the elongate member. Other devices include a signalgenerator for controlling the activation of the SMA actuators.

The lumen(s) can also be used to flush the distal end of the ultrasounddevice with fluid. This fluid can improve the ultrasound signal, can beused to flush the area around the IVUS imaging device to ensure that thearea is free of debris or bubbles which would interfere with theperformance of the ultrasound device, and cool the ultrasound transducerand/or the SMA actuators. In an embodiment with using one or more lumensto flush the distal end of any of the devices described herein, it isdesirable to provide a means for the fluid to circulate through the areaaround the ultrasound transducer, such as another lumen to return thefluid to the proximal end of the elongate member, or an opening in thedistal end of the elongate member so that the fluid can escape.Optionally, a fluid pump can be attached to the proximal end of theelongate member to facilitate fluid circulation through the lumen(s). Inanother embodiment, the distal end of the elongate member contains fluidwhich is sealed or injected in the distal end and/or a lumen of theelongate member.

In another embodiment, SMA actuators can be used to bend or steer thedistal end of the elongate members disclosed herein to allow the user toreduce the distance between the distal end of the device and imagetarget. In the case of intravascular OCT this reduces the artifactcaused by blood between the image acquisition device and the vessel wallby bringing the imaging portion of the device closer to the wall itself.Similar to current intravascular ultrasound system (IVUS), localactuators can provide the pull-back motion of the imaging tip, so it cancontrol precisely the pull-back of the distal imaging tip and generatethree-dimensional images of the blood vessel.

As discussed above, the angle or orientation of the ultrasoundtransducer or reflector, or the OCT reflector or prism can determinewhere the imaging energy is directed. For some applications, theseelements direct the energy generally orthogonally from the longitudinalaxis of the device. For other applications, these elements can beoriented to direct the imaging energy toward the distal tip of thedevice, resembling forward looking devices, or toward the proximal endof the device. In another embodiment of the invention, an additional SMAactuator is incorporated into the device to actively move thetransducer, reflector or prism and change the imaging plane adaptively.This active angle control can provide side-looking and forward-lookingas needed with a single imaging device.

In another embodiment, the IVUS system described herein and the OCTdevice described herein are combined in a single elongate member toprovide both IVUS and OCT imaging in a single, compact device.

Although the embodiments described herein have the imaging deviceslocated in the distal end of the elongate member, one of skill in theart will recognize that the imaging devices can be placed anywhere alongthe length of the elongate member.

In another embodiment, the imaging devices disclosed herein areintegrated into the distal end of a guide wire's rigid section, butproximal to the coil structure that defines the distal tip of aguidewire.

In another embodiment, the imaging devices described herein are combinedwith one or more therapeutic or interventional devices, for example, butnot limited to, devices for stent placement and deployment, balloonangioplasty, directional atherectomy, cardiac ablation, PFO (patentforamen ovule) closure, transvascular re-entry, trans-septal punch, andCTO (chronic total occlusion) crossing.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention can be practiced in many ways.As is also stated above, it should be noted that the use of particularterminology when describing certain features or aspects of the inventionshould not be taken to imply that the terminology is being re-definedherein to be restricted to including any specific characteristics of thefeatures or aspects of the invention with which that terminology isassociated. The scope of the invention should therefore be construed inaccordance with the appended claims and any equivalents thereof.

What is claimed is:
 1. An intravascular imaging device, comprising: anelongate member having a proximal portion and a distal portion; anactuator mechanism disposed adjacent the distal portion of the elongatemember, the actuator mechanism comprising a first anchor, a secondanchor, at least one movable element, a deformable component, and afirst Shape Memory Alloy (“SMA”) actuator, and an imaging elementconnected to the at least one movable element; wherein the first anchoris connected to a first side of the at least one moveable element by thefirst SMA actuator and the second anchor is connected to a second sideof the at least one movable element by the deformable component; whereinthe first and second anchors are secured relative to the elongatemember; wherein a longitudinal axis of the actuator mechanism extendingbetween the first anchor and the second anchor is substantially parallelto the longitudinal axis of the elongate member; wherein the first SMAactuator has an activated state and a deactivated state; and wherein theat least one movable element and the imaging element move in a firstdirection relative to the elongate member upon activation of the firstSMA actuator.
 2. The device of claim 1, wherein the deformable componentcomprises a second SMA actuator.
 3. The device of claim 2, wherein thesecond SMA actuator has an activated and a deactivated state and whereinthe at least one movable element and the imaging element move in asecond direction relative to the elongate member upon activation of thesecond SMA actuator following deactivation of the first SMA actuator,the second direction being counter to the first direction.
 4. The deviceof claim 3, wherein the first and second directions are rotational aboutthe longitudinal axis of the elongate member.
 5. The device of claim 3,wherein the first and second directions are translational substantiallyparallel to the longitudinal axis of the elongate member.
 6. The deviceof claim 1, further comprising a second imaging element connected to theat least one movable element.
 7. The device of claim 1, wherein theimaging element is an ultrasound transducer.
 8. The device of claim 1,wherein the imaging element is an optical coherence tomography (OCT)element.
 9. The device of claim 1, wherein the imaging element is areflector.
 10. The device of claim 1, wherein the imaging element is aprism.
 11. An intravascular imaging apparatus, comprising: an elongatemember having a proximal portion and a distal portion; an imagingelement disposed in the distal portion of the elongate member; and anactuator mechanism disposed in the distal portion of the elongate memberand configured to provide cyclical motion to the imaging element,wherein the actuator mechanism comprises a first anchor, a secondanchor, a movable element, a Shape Memory Alloy (“SMA”) actuatorconnected to the first anchor and a first side of the movable element,and a deformable component connected to the second anchor and a secondside of the movable element, wherein the first and second anchors arefixedly secured to the elongate member and wherein a longitudinal axisof the actuator mechanism extending between the first anchor and thesecond anchor is substantially parallel to the longitudinal axis of theelongate member, wherein the imaging element is coupled to the movableelement.
 12. The apparatus of claim 11, wherein the imaging element issecured to the movable element of the actuator mechanism.
 13. Theapparatus of claim 11, further comprising a second SMA actuator coupledto the second anchor and the movable element.
 14. The device of claim11, wherein the cyclical motion includes rotation about the longitudinalaxis of the elongate member in two opposing directions.
 15. The deviceof claim 11, wherein the cyclical motion includes translation along thelongitudinal axis of the elongate member in two opposing directions. 16.The device of claim 11, wherein the imaging element is an ultrasoundtransducer.
 17. The device of claim 11, wherein the imaging element isan optical coherence tomography (OCT) element.
 18. An intravascularimaging apparatus, comprising: an elongate member having a proximalportion and a distal portion; an actuator mechanism disposed within thedistal portion, the actuator mechanism including: a first anchor fixedlyattached to the elongate member, a second anchor fixedly attached to theelongate member and spaced from the first anchor, a movable elementpositioned between the first and second anchors, a first Shape MemoryAlloy (“SMA”) actuator connected to the first anchor and the movableelement, and a second Shape Memory Alloy (“SMA”) actuator connected tothe second anchor and the movable element, wherein a longitudinal axisof the actuator mechanism extending between the first anchor and thesecond anchor is substantially parallel to a longitudinal axis of saidelongate member, and wherein selective activation and deactivation ofthe first and second SMA actuators imparts oscillatory motion to themoveable element; and an imaging element coupled to the movable element.19. The apparatus of claim 18, wherein the imaging element is anultrasound transducer.
 20. The apparatus of claim 18, wherein theimaging element is an optical coherence tomography (OCT) element.